It is often necessary or desirable to measure various blood parameters, such as blood gases, pH, hematocrit, oxygen saturation, etc. This can be accomplished in real time by passing blood through a cuvette and directing one or more appropriate optical signals through an optical window toward the blood in the cuvette. An optical signal is provided by the blood parameter of interest which can be used to measure this blood parameter in accordance with known techniques. Specific examples of a cuvette for measuring blood oxygen saturation and hematocrit are shown in Heinemann U.S. Pat. No. 4,444,498 and Karkar et al U.S. Pat. No. 4,745,279, respectively.
In the case of measuring hematocrit or blood oxygen saturation, the cuvette is coupled to an instrument which provides light at appropriate wavelengths for directing through the optical window and into the blood in the passage of the cuvette. The blood returns a portion of this light in the form of an optical signal back to the instrument where it is appropriately processed to determine hematocrit and/or oxygen saturation.
In order that accurate data is obtained, it is essential that the cuvette be properly optically coupled to the instrument. Without proper optical coupling, there may be a loss of optical signal which would yield an inaccurate measurement of hematocrit or oxygen saturation. For example, the cuvette may be nearly, but not completely, coupled to the instrument in such a way that it would appear to the attendant that proper coupling was achieved. This, however, would provide inaccurate measurements due to signal loss and/or admission of ambient light into the signal path.
Another factor which, by way of example, might provide for a degradation in accuracy results from the use of unauthorized cuvettes. An unauthorized cuvette may not properly mate with the instrument or optical head or its optical path may have different characteristics that may introduce error into the calculations.
It would also be desirable to be able to automatically provide information about the cuvette to the instrument. Although this could be provided manually by an attendant, doing so automatically eliminates the possibility of attendant error. One example of this would be to provide information to the instrument as to the diameter or cross-sectional area of the passage through the cuvette so that the instrument would know, for example, if the cuvette were 3/8 or 1/2 inch in diameter. With this information, the instrument could then utilize the appropriate algorithm and/or terms in an algorithm to properly calculate hematocrit and/or blood oxygen saturation.